D. Bo6et, J. Vauclair/Beha6ioural Brain Research 109 (2000) 143-165
159
already familiarised with photographs, was able to dis-
criminate the orientation of photographs. In addition,
it was shown that experience with a particular place did
not facilitate the discrimination between that location
and another. Finally, it was shown that when tested
with a natural concept (food), pigeons transferred a
discrimination from object to picture and vice versa,
but they did not demonstrate such transfer when they
were tested with an arbitrary pseudoconcept. In brief,
the experiments summarised in this section highlight the
importance of biological relevance in picture recogni-
tion tasks.
Table 4 presents an outline of the investigations that
demonstrated a failure to recognise pictures in animals.
6. Conclusion
One of the main conclusions of this survey is that
visual stimuli presented as pictures (either as black-and-
white photos, colour photos, slides, or videos) are not
necessarily immediately recognised by non-human and
even human subjects. In this final section, we will
summarise the principal results concerning picture
recognition in the much-studied species and attempt to
identify some of the factors which may be responsible
for the apparent difficulties in recognising pictorial
stimuli. Finally, we will suggest some possible steps
which could be useful in describing picture processing;
ranging from feature discrimination, to correspondence,
and ultimately, to strict equivalence between a 3-D
object and its pictorial representation and a consider-
ation of the issue of confusion between pictures and the
objects they represent.
6.1. Summary of main findings
Very young humans appear to be able to recognise
photographs from 2 or 3 months of age and at an even
earlier age they are likely to discriminate real objects
from their pictorial representations. Paradoxically, pic-
ture recognition seems to present greater difficulties for
adults who are unaccustomed to seeing photographs
and drawings. Thus, it could be hypothesised that such
an ability is innate but that this ability diminishes if the
person has grown up without opportunities to see 2-D
representations. In this case (which is less and less likely
to happen in contemporary societies), such individuals
are accustomed to seeing the world of objects around
which are inevitably characterised by the presence of
features like colours, depth, and motion parallax; when
presented with pictures, these people, who have lived in
an exclusively 3-D environment, would experience
difficulties and some familiarity and/or training with
pictures would then be required in order to recognise
the stimuli which lack those features.
The available literature is quite convincing concern-
ing the abilities of several animal species familiar with
pictures to recognise such 2-D stimuli. In mammals in
general (but with most evidence coming from experi-
ments conducted with monkeys and apes), it also seems
that picture recognition is possible for both adults and
young even if the animals have never been exposed to
any picture prior to the experiment. In this latter case,
recognition seems to be more difficult and appears to
depend on the nature of stimuli and on the experimen-
tal conditions (see below). Some experiments, in which
subjects have to transfer what they have learned with
real objects to the pictures of these objects (e.g. in
cross-modal transfer between touch and vision), have
shown that these tasks present serious difficulties for
the subjects. Furthermore, because some training is
often necessary in order to perform picture recognition
tasks, the training phase probably allows subjects to get
familiarised with pictures prior to testing; this require-
ment implies that subjects are rarely naive with respect
to viewing pictures or their discrimination.
The studies reporting spontaneous responses to pic-
tures are interesting because they can provide useful
indications on the perceptual and cognitive processes
involved in picture recognition performed by truly
naive subjects. These studies have shown that monkeys
and other mammals (sheep and dogs) can, at first sight,
adaptively respond to various animals or foods (al-
though pictures of conspecifics seem to be responded
more easily to than pictures of other categories of
stimuli) presented on slides. We can speculate that this
ease presumably expresses the fact that these animals
confuse the real objects and their pictures; nevertheless,
this recognition can be quite precise, if we consider that
some animals are able (e.g. [4]) to differentiate individu-
als from their own breed from individuals belonging to
other breeds. It is also worth noting that transfer is
generally better for pictorial stimuli which better match
(at least for a human viewpoint) real objects, that is,
motion films are more easily recognised than still pic-
tures, slides are better recognised that colour photo-
graphs, the latter leading to better performance
compared to black-and-white photographs and line
drawings.
It may be an interesting observation that in the first
section of our review (convincing demonstrations),
studies concerning mammals are more numerous than
studies concerning birds, and that the opposite is true
of the third section (difficulties with picture recogni-
tion). Actually, the pattern of results obtained with
birds is quite different compared to other zoological
groups; a divergence which may be explained in part by
the fact that bird vision is different from mammal
vision. With regard to pictures, photographs used in
experiments with these animals are usually matched for
human vision and lack some critical features of birds’